1. Field of the Invention
The disclosure relates to a radio frequency (RF) sensing circuit, and more specifically, to an RF sensing circuit having a voltage-controlled oscillator.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Current RF sensing circuits may be classified into two types including an independent power detector and an architecture using a traditional RF receiver associated with a digital signal processor. For an independent power detector, a circuit sensing signal power is formed at the front end of the RF. This architecture is simple but is not sensitive, and requires serial connection of multiple amplifiers to satisfy the system requirement. In such an arrangement, signals are easily obscured by noises. Hence, this architecture is restricted to certain applications. For the architecture using a traditional RF receiver associated with a digital signal processor, a heterodyne-type reception portion (including a low noise amplifier, a first mixer, a first intermediate frequency amplifier, a second mixer, a second intermediate frequency amplifier and two sets of frequency synthesizers) at the second intermediate frequency end verifies noises and signals by an analog-to-digital converter and the digital signal processor to sense the presence of sensing signals. For an RF sensing circuit, the base band end and the reference signal embedded in the digital signal processor are compared to judge the presence of the signals. Although the sensitivity of such sensing circuit can meet the system requirement, the sensing circuit is complex and has high power consumption, and the circuit dimensions are not easily decreased. Moreover, the architecture is generally restricted by the switching timing of the frequency synthesizer of the reception portion and it is not easily possible to increase the frequency spectrum scanning speed of the sensing circuit. Hence, this architecture needs a high sampling rate analog-to-digital converter and a high-speed and high-capacity digital signal processor to perform complex sampling, calculation and comparison, and thus the cost is relatively high.